What Can Cherry Blossoms Tell Us About Climate Change?

April 8, 2011

This weekend, the National Cherry Blossom Festival in Washington, D.C. wraps up, with organizers promising that Saturday's Cherry Blossom Parade will go ahead even if the federal government shuts down. The festival, a Washington springtime tradition since the 1930s, regularly draws thousands of attendees, and "brings in at least $126 million to the D.C. metro area each year, according to the National Park Service, making it the city’s largest annual tourism event by far." As popular as the cherry blossom is in the United States--many cities and towns now hold their own cherry blossom festivals--in Japan, the cherry blossom is associated with both the goddess of Mount Fuji in Japanese mythology, and with samurai culture. More recently, just as American meteorologists report on leaves "turning" in the fall, Japanese meteorologists follow the blossoming in the spring. This begs the question: since the blossoming is tied to the temperature, can the cherry blossom tell us anything about climate change?

Yes, says Dr. Yasuyuki Aono of the Osaka Prefecture University. Since the mid-1990s, Aono and his colleague Yukio Omoto have been unearthing records of cherry blossom festivals in the former capital of Kyoto and nearby towns going back to the 9th century. Using the dates of the festival given in the records, and an equation that calculated the temperature in March of a given year based on when the cherry blossoms flowered, Aono was able to estimate March temperatures in the Kyoto area for the past 1200 years, a full thousand years farther back than most temperature data is available for.

The findings would not please climate change deniers: Aono found that recent flowering days are earlier than any in the past 1200 years. In addition, Aono found that the coldest periods in the last century coincided "with periods of low activity in the long-term solar cycle" (represented by the gray areas in the first graph below), but since 1950 the temperature cycle has diverged from tracking sun activity.